Just more on what filesosofo said, Basically, The plugin is using more memory than is currently allocated to WordPress.

You can increase the memory WordPress allocates for itself byu adding define('WP_MEMORY_LIMIT', '64M'); to your wp-config.php file. The plugin should really do things more efficiently perhaps, but if you use muliple plugins which use a lot of memory, sometimes you need to increase that limit.

Increasing the limit does not work all webhosts, some lock you to a certain limit.